The long term objective of this proposal is to understand the connection between the basic defect in CF and the predisposition of CF patients to P. aeruginosa infections. The proposal builds on preliminary work, which demonstrated that epithelial cells expressing a mutant CFTR gene have an impaired ability to ingest P. aeruginosa, compared to cells that express wild-type CFTR. Further work has demonstrated that a small exposed loop in CFTR is the receptor for a bacterial ligand, which is the oligosaccharide core component of LPS. Paradoxically, the core also stimulates expression of CFTR in cells, and therefore increases bacterial ingestion. The amino acid domains in the receptor portion of CFTR will be determined by use of a series of short peptides and peptides carrying amino acid substitutions. The role of the CFTR in uptake of P. aeruginosa will be determined using mice that express different alleles of CFTR, some of which differ in the level of expression of the putative bacterial adhesin. The protective effect of the bacterial core oligosaccharide on infection will be examined, using a neonatal mouse infection model, where clearance of P. aeruginosa should be correlated with pretreatment of the animals with the LPS ligand. Moreover, if an increased bacterial clearance can be demonstrated in mice with defective CFTR, the results of these studies should provide a new candidate therapeutic agent for the treatment of P. aeruginosa respiratory infections in humans.